can't say I like this idea, because 99.9% users don't need this.
there is exists a number of open source dreamcast emulators, why not add vertex counter in one of them ? this would be easy task for person who have even "junior" coding skills.

add: if you need information about few specific games - I can provide it.
btw with S-16 topic you was referring to ?

DoA2 25000 - 35000 (@60fps), most (if not only) really optimized DC game I'd say.
F355 7000 - 16000, usually about 12000 (@60fps)
Shenmue II during game about 10000 - 15000, in some scenes up to 25000 (@30fps)
Le Mans during track 8000 - 9000, ~25000 at start then all opponent cars and tribunes visible (@30fps)

speaking in general - DC's GPU may render way more polygons, and it may look way better if vertex colors had applied nice lighting, but DC CPU was too weak to transform significant amounts of geometry and calculate good lighting effects.

PS: note - numbers is vertex counts, it is some less than actual triangle polygons count.

Appreciate the information. Yea I've heard thats exactly the reason why so many Dreamcast games have poor lighting and shadows, because it has to be processed by the Hitachi SH4, which is already busy doing geometry calculations and physics. The PS2 doesn't suffer from this as much because it has co-processors(Vector Unit 0 & 1).

IMHO the actual reasons was:
- games was looking cool enough for its time (1999 - 2000), and customers was like "shut up and take my money" already. so, from developer/publisher perspective, there was no reason to waste time and resources = money and make games better (like making high-polygon models and higher resolution textures).
- developers was not really interested in learn & use Dreamcast hardware specific/exclusive features. instead they use mostly feature set they familiar with, and in the way, how they used to use it for other hardware platforms. (this is not assumption, but fact based on information from Sega staff and former game developers)

so, the reasons mostly not technical, but more like lack of developers motivation to make games which pushes Dreamcast hardware up to its limits.
even if Dreamcast was weaker compared to PS2, there very few games really uses its full raw power (like DoA2), and none of games uses all "non common / exclusive" hardware features.